The flux of cosmic rays to the atmosphere has been reported to correlate
with cloud and aerosol properties. One proposed mechanism for these
correlations is the "ion-aerosol clear-air" mechanism where the cosmic
rays modulate atmospheric ion concentrations, ion-induced nucleation of
aerosols and cloud condensation nuclei (CCN) concentrations. We use a global
chemical transport model with online aerosol microphysics to explore the
dependence of CCN concentrations on the cosmic-ray flux. Expanding upon
previous work, we test the sensitivity of the cosmic-ray/CCN connection to
several uncertain parameters in the model including primary emissions,
Secondary Organic Aerosol (SOA) condensation and charge-enhanced
condensational growth. The sensitivity of CCN to cosmic rays increases when
simulations are run with decreased primary emissions, but show
location-dependent behavior from increased amounts of secondary organic
aerosol and charge-enhanced growth. For all test cases, the change in the
concentration of particles larger than 80 nm between solar minimum (high
cosmic ray flux) and solar maximum (low cosmic ray flux) simulations is less
than 0.2 %. The change in the total number of particles larger than 10 nm
was larger, but always less than 1 %. The simulated change in the
column-integrated Ångström exponent was negligible for all test
cases. Additionally, we test the predicted aerosol sensitivity to week-long
Forbush decreases of cosmic rays and find that the maximum change in aerosol
properties for these cases is similar to steady-state aerosol differences
between the solar maximum and solar minimum. These results provide evidence
that the effect of cosmic rays on CCN and clouds through the ion-aerosol
clear-sky mechanism is limited by dampening from aerosol processes.